Re: [PATCH v2] ceph: invalidate pages when doing DIO in encrypted inodes

[Xiubo Li]

On 4/6/22 6:57 PM, Luís Henriques wrote:
> Xiubo Li <xiubli@xxxxxxxxxx> writes:
>
> > On 4/1/22 9:32 PM, Luís Henriques wrote:
> > > When doing DIO on an encrypted node, we need to invalidate the page cache in
> > > the range being written to, otherwise the cache will include invalid data.
> > >
> > > Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
> > > ---
> > >    fs/ceph/file.c | 11 ++++++++++-
> > >    1 file changed, 10 insertions(+), 1 deletion(-)
> > >
> > > Changes since v1:
> > > - Replaced truncate_inode_pages_range() by invalidate_inode_pages2_range
> > > - Call fscache_invalidate with FSCACHE_INVAL_DIO_WRITE if we're doing DIO
> > >
> > > Note: I'm not really sure this last change is required, it doesn't really
> > > affect generic/647 result, but seems to be the most correct.
> > >
> > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > > index 5072570c2203..b2743c342305 100644
> > > --- a/fs/ceph/file.c
> > > +++ b/fs/ceph/file.c
> > > @@ -1605,7 +1605,7 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
> > >    	if (ret < 0)
> > >    		return ret;
> > >    -	ceph_fscache_invalidate(inode, false);
> > > +	ceph_fscache_invalidate(inode, (iocb->ki_flags & IOCB_DIRECT));
> > >    	ret = invalidate_inode_pages2_range(inode->i_mapping,
> > >    					    pos >> PAGE_SHIFT,
> > >    					    (pos + count - 1) >> PAGE_SHIFT);
> > The above has already invalidated the pages, why doesn't it work ?
> I suspect the reason is because later on we loop through the number of
> pages, call copy_page_from_iter() and then ceph_fscrypt_encrypt_pages().

Checked the 'copy_page_from_iter()', it will do the kmap for the pages 
but will kunmap them again later. And they shouldn't update the 
i_mapping if I didn't miss something important.

For 'ceph_fscrypt_encrypt_pages()' it will encrypt/dencrypt the context 
inplace, IMO if it needs to map the page and it should also unmap it 
just like in 'copy_page_from_iter()'.

I thought it possibly be when we need to do RMW, it may will update the 
i_mapping when reading contents, but I checked the code didn't find any 
place is doing this. So I am wondering where tha page caches come from ? 
If that page caches really from reading the contents, then we should 
discard it instead of flushing it back ?

BTW, what's the problem without this fixing ? xfstest fails ?


-- Xiubo

> Cheers,